Oil Cooling System Plumbing

First, the disclaimer. There are a few differences in this plumbing from the original KISS design, which you will see in the pictures below. I made minor changes to the oil cooler arrangement and M/R gear box oil filter location. Also, I replaced the KISS M/R gear and Rotax C gear chip detectors with a pair of my own design. The flow path though, for all three of the oil cooling systems, still remains the same.

I did however make a fairly significant change to the turbine fuel flow path from the original turbine and KISS design, by re-plumbing the turbine's normally-closed "Run Fuel" solenoid valve to serve as a "Fuel Pressure Release" valve, as suggested by other builders. I also relocated the solenoid valve, the two fuel pressure senders and the turbine oil pressure sender and oil pressure switch to a small containment box with the fuel pump, to tidy-up some of the plumbing and electrical routing. I'll focus on the gear box and oil cooler plumbing here, and cover the fuel system plumbing in greater detail separately.

In this picture taken from beneath the rear of the helicopter, you can see the three oil coolers assembled. The M/R gear oil filter and large oil cooler are mounted forward (left in photo) toward the fuel tank. The Rotax C and turbine oil coolers are mounted side by side toward the rear, with the Rotax C oil cooler on the port side (top in photo) and the Turbine oil cooler mounted on the starboard side. The cooling fan fits completely over the M/R cooler and partially over both of the Rotax and Turbine coolers, as shown in some of the later photos below. The three KISS kit coolers came with AN6 male fittings installed.

(Note: You can click on these pictures to view in higher resolution.)

With the seat back removed, here is the front of the M/R gear box, with the cooling oil pump installed at the bottom of the M/R shaft. (I've since modified the cooling pump attachment several times, see additional pictures below.)

Left side of the M/R gear box, showing the 1/4" clear FEP teflon tubing oil level sight tube, with 1/4" tubing x 1/8" MPT elbow brass fittings. Make sure you use a brass or steel insert inside the ends of the FEP tubing or the fittings will leak.

The KISS-supplied vent filter is installed on top of the gear box with a 3/8" hose barb x 1/4" MPT connector and a hose clamp. A 1/4" NPT plug fitting (not shown) is also used to plug the 1/4" oil fill port on top of the gear box.

Here is the right side of the M/R gear box, showing the oil outlet connection at the bottom of the gear box and the oil return connection on top. Both connections to the gear box use a 3/8" NPT x 6AN male straight fitting. The top return fitting is a 3/8" hose x 6AN female 150o hose end. The M/R gear box temp sender and the thermostat switch are installed just above the bottom outlet tee, below.

Attached to the bottom outlet fitting is a 6AN female x 6AN male branch tee, with a chip detector in the near end and a 6AN female 90o hose end on the other.

(Note: The original 162F M/R shaft bolts are shown; these will be replaced with the proper (shorter) bolts later.)

This is the chip detector fitting, made from a 6AN cap threaded for an AN4 bolt like the one shown beneath. The AN4 bolt was drilled through; it contains the chip detector magnet with a #6 screw thread attached, which are centered, insulated and sealed inside the bolt with epoxy. The bolt is also sealed into the AN6 cap with epoxy. You can view the design drawing here.

The chip detector can be installed inside any standard 6AN tee or straight fitting. The red terminal lug connects through to the magnet; the blue terminal lug must be used to ensure a good ground connection when using the anodized aluminum fittings.

Rather than suspendending the oil filter from the bottom of the M/R gear box as per the KISS instructions, I mounted it instead down on front of the oil cooler as shown here. Hopefully this will help keep oil off of everything up above.

The hose from the M/R gear box chip detector tee routes down along the right side of the helicopter into the inlet side of the filter housing.

The oil filter outlet hose routes from the top of the oil filter forward, to the bottom inlet port on the oil pump.

The oil pump came with 4 8AN inlet and outlet connectors. I replaced those with 4 6AN (male x 9/16"-18 o-ring boss) straight connectors instead. Off to the right of the oil pump is a long 3/4" steel strap intended to prevent the oil pump from turning.

The aluminum box on top of the tank (beneath the alternator) is just a small terminal box I installed around the fuel tank level sensor.

Later, I replaced the strap that prevents the oil pump from turning with the 0.062 4130 CrMo brackets shown here. Then of course the rigid KISS aluminum shaft coupler and my new rigid pump mounting brackets really fought each other, so I had to replace the Al coupler with something more flexible.

The KISS Al coupler bolted on the outside bottom of the M/R shaft. I replaced the Al coupler with a smaller Al plug that fits partially up inside the hollow M/R shaft (same 1/4" bolt hole), then shortened the oil pump shaft to 1" long.

A short section of 5/8" ID rubber hose and two hose clamps connect the new plug to the pump, which runs much smoother now.

The oil pump outlet hose routes from the bottom outlet of the oil pump, back to the left forward end of the M/R gear box (front) oil cooler. The oil then returns out of the right forward end of the cooler back up the right side to the top of the M/R gear box, as shown in the pictures above.

The Rotax C gear box cooling system is almost identical to the M/R oil system, except that an oil filter is not used. Connections to the top and bottom of the housing are made using 18mm x 1.5mm o-ring boss x 6AN fittings. The oil temperature sensor screwed into the side of the housing is a Westberg 399S1 1/8" NPT fitting with a 5/16" end.

The gear box has two ports available on the side for the oil level sight tube and vent. Unfortunately, they are tapped for a 1/4-28 straight male o-ring boss, which I could not easily find. Instead I made the fittings shown here (Banjo style) using AN4 bolts, drilled internally and some standard brass 1/4" compression fittings.

The oil level is filled to the input shaft centerline. The oil return line installed at the top of the Rotax housing should cover the output gear and shaft bearings.

Here is the chip detector tee beneath the Rotax gear box. When I first installed the chip detector, it measured several M-ohms resistance. It collected enough fine gear dust after the first few engine runs though to short it completely.

Fortunately, the chip detector can be removed easily for cleaning, with only a few cc's of oil loss if you quickly cork the tee. An old foam ear plug works well. To restore the chip detector, I used solvent and a rag to remove the oil, then masking tape to pull all the fine metal dust from the magnetic gap.

Looking from the opposite side, the 3/8" hose from the chip detector tee routes forward alongside my (offset) "center" square tube and down to the top inlet port on the right side of the oil pump.

The oil pump outlet hose routes from the top outlet of the oil pump, down to the forward end of the left (Rotax gear box) oil cooler. The oil return hose leaves the back end of the oil cooler and routes up along the left side diagonal frame tubes to the top of the Rotax gear box, where it connects with a 6AN female 120o hose end.

The turbine gear box is somewhat different in that it has its own internal oil pump, filter and chip detector. It still requires an external oil cooler though. The oil inlet and outlet ports, which are located on the left side of the turbine, require a pair of 5AN (1/2"-18 o-ring boss) by 6AN male connectors. The vent filter can just be seen on top of the turbine; it is connected with a 3/8" hose barb x 6AN female fitting.

The cooling oil outlet port on the turbine is actually located above the oil return port. The 6AN male branch tee shown on the outlet fitting holds the turbine oil temperature sensor. The upper end of the tee was cut off, then drilled and tapped for the Westberg 399S1 1/8" NPT fitting with a 5/16" end.

In the fittings spreadsheet I listed the oil return hose fitting as a 6AN female 90o hose end. The fitting shown here is actually a 6AN female 120o hose end, which I pulled outward to clear the frame tube, to accomodate the lower engine installation.

The turbine oil cooler is located on the back right side of the three-cooler assembly. I would liked to have positioned it on the left side directly beneath the turbine inlet and outlet ports, but the right side of the helicopter seemed to offer the best overall routing for both the turbine and the Rotax C oil hoses. Both of the turbine oil hoses connect to the cooler with a 6AN female 90o hose ends.

Here is another view of the three oil coolers, from just beneath the rear of the helicopter. If you would like a better idea of how these were mounted, there is a better explanation and pictures on the Rotorway Owner's Group Forum here.

This pretty much wraps it up for the three main gear boxes and oil cooling systems. The fuel system plumbing is discussed on a separate web page here. A complete list of the plumbing fittings used for both the oil cooling and fuel systems, including part numbers and current pricing, can be downloaded here.